Valve for fuel cell based power generator

ABSTRACT

A device has an annulus having a first end and a second end. A valve plate is coupled to the first end of the annulus by a fastener, wherein the valve plate is adapted to contact a valve seat on a hydrogen producing fuel cover. A diaphragm is coupled to the second end of the annulus by a fastener, wherein the annulus extends through a container for holding the hydrogen producing fuel and wherein the diaphragm moves the valve plate relative to the valve seat responsive to a different in pressure across the diaphragm.

RELATED APPLICATIONS

This application is related to the following two applications filed onthe same date herewith: Fuel Cell Based Power Generator (ApplicantReference Number: H0019541) and Method of Manufacturing Fuel Cell BasedPower Generator (Applicant Reference Number: H0020226).

BACKGROUND

Proton exchange membrane (PEM) fuel cells use a simple chemical reactionto combine hydrogen and oxygen into water, producing electric current inthe process. Hydrogen may be produced by a chemical reaction between afuel, such as lithium aluminum hydride and water vapor. At an anode,hydrogen molecules are ionized by a platinum catalyst, and give upelectrons. The PEM allows protons to flow through, but not electrons. Asa result, hydrogen ions flow through the PEM to a cathode, whileelectrons flow through an external circuit. As the electrons travelthrough the external circuit, they can perform useful work by poweringan electrical device such as an electric motor, light bulb or electroniccircuitry. At the cathode, the electrons and hydrogen ions combine withoxygen to form water. The byproducts of the reaction are water and heat.

In some prior PEM fuel cell based power generator, a pneumatic valve isused to control a hydrogen generating chemical reaction that feedshydrogen oxygen PEM fuel cells. The valve comprises a substantialportion of the power generator volume and weight, and thus reduces theenergy density and specific energy of the power generator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a power generator according to an exampleembodiment.

FIG. 2 is an enlarged block diagram of a portion of the power generatorof FIG. 1.

FIG. 3A is a top view of a segment of a fuel cell membrane patternaccording to an example embodiment.

FIG. 3B is a top view of a ring shaped adhesive pattern according to anexample embodiment.

FIG. 3C is a top view of a cathode metallization pattern according to anexample embodiment.

FIG. 3D is a top view of a finished cathode electrode that includesmultiple sections for contacting multiple fuel cell membrane segmentsaccording to an example embodiment.

FIG. 3E is a top view of an anode metallization pattern used to form ananode electrode according to an example embodiment.

FIG. 3F is a top view of an anode electrode formed from the pattern ofFIG. 3E.

FIG. 4 is a cross sectional block schematic diagram illustratingelectrical connections between segments of fuel cell stacks according toan example embodiment.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings that form a part hereof, and in which is shown by way ofillustration specific embodiments which may be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention, and it is to be understood thatother embodiments may be utilized and that structural, logical andelectrical changes may be made without departing from the scope of thepresent invention. The following description of example embodiments is,therefore, not to be taken in a limited sense, and the scope of thepresent invention is defined by the appended claims.

Various embodiments of a PEM fuel cell based power generator of variousshapes are described. In one embodiment, the power generator is formedwith the shape of a CR2032 battery, which is commonly used in watches,sensors and other electronic equipment. Such reduced height form factormay be achieved by one or more of several innovative features describedherein.

FIG. 1 is a cross section block diagram of a power generator 100according to an example embodiment. FIG. 2, is a blown up cross sectionblock diagram view of one side of the power generator 100, withnumbering consistent with FIG. 1. Power generator 100 has a container110 adapted to hold a hydrogen generating fuel. The container may becylindrical or rectangular in shape. Many other shapes, such as otherpolygons may be used as desired. A valve assembly having a valve plate112 has a border that fits within a border of the container 110. A fuelcell 114, having multiple segmented fuel cells connected in series asdescribed in further detail below, is laterally disposed outside andaround the valve assembly. The fuel cell 114 has a lateral width thatfits within the border of the container 110. A cover indicated generallyat 115 is adapted to mate with the container 110 and enclose the valveplate 112 and fuel cell 114. Many of the components of power generator100 may be formed of stainless steel 316, or nickel plated steel. Othermaterials may also be used in further embodiments that provide suitableconductive, corrosion resistant and structural properties.

In one embodiment, the fuel cell is ring shaped, with multiple fuelcells electrically coupled with one another. In one embodiment, the fuelcell comprises five arc shaped fuel cells, referred to as fuel cellsegments, serially coupled to form a full circular fuel cell. Othershaped fuel cells may be used with different power generator shapes infurther embodiments, such as a straight or angled segments for polygonshaped power generators. Each fuel cell segment in one embodimentproduces approximately 0.6 V under load, for a total of 3V. The fuelcell has multiple layers extending radially from outside the valve plate112. Fuel cell 114 in one embodiment is a proton exchange membrane (PEM)type of fuel cell.

In one embodiment, a portion of the cover 115 is electrically coupled tothe fuel cell 114 to form an anode cap 118 via an anode tab 120, and thecontainer 110 is electrically coupled to the fuel cell 114 to form acathode via a cathode tab 122, which may be adhesive backed in oneembodiment. Cover 115 in one embodiment comprises anode cap 118 coupledto a fuel cap 124. The anode cap 118 and fuel cap are electricallyinsulated from each other by an insert 126. In one embodiment, theinsert 126 may be formed of PET (polyethylene terephthalate). Otherelectrically insulative materials may also be used in furtherembodiments.

In one embodiment, the power generator 100 container 110 and cover 115when assembled define a low height cylindrical exterior of the powergenerator and have dimensions compatible with a CR2032 battery formfactor having an outer diameter of approximately 20 mm and height ofapproximately 3.2 mm. The anode cap diameter is approximately 16.5 mm inthis embodiment. The power generator 100 may be formed with many otherdimensions. Power generator 100 is well suited to lower height designsdue to the ability to form both the valve plate and fuel cell in asimilar planar region above the fuel container 110 defined by the cover115. The term, “diameter” refers to the distance between opposingborders, and may be used for cylinders or power generators of othershapes.

In one embodiment, the fuel cap 124 has a valve seat 128 positionedlaterally inside the fuel cell 114 and formed to mate with the valveplate 112 to regulate flow of water vapor generated by the fuel cell 114to fuel 130 contained within the container 110. PTFE (Polytetrafluoroethylene) or other suitable material may be used at the interfacebetween the valve seat 128 and valve plate 112 to prevent stiction andto provide a better seal.

In one embodiment, the valve assembly includes a valve stem assembly 132coupled to the valve plate 112 at a first end, extending through anopening in the fuel container 110 defined by a side wall 134. The valvestem assembly 132 is coupled to a diaphragm 136 at a second end. Thediaphragm 136 is retentively coupled to the fuel container by adiaphragm support 138 fastened to the container within a recess of thecontainer indicated at 140. The use of such a recess provides a fairlyflat bottom of the container, which in some embodiments may beconsistent with a CR2032 form factor battery. In one embodiment, thediaphragm support 138 is electrically coupled to the container 110 andalso serves as part of the cathode. The diaphragm support 138 has anopening 142 proximate the diaphragm 136 such that a difference inpressure across the diaphragm 136 controls the position of valve plate112. In one embodiment, a bottom end of the valve stem assembly 132 isrecessed within the recess 140 such that motion of the diaphragm willnot result in movement of the bottom of the valve stem assembly beyondthe bottom of the container 110.

The use of a recess 140 for the diaphragm 136, combined with the use ofa diaphragm 136 having a smaller border than the fuel container 110,allows for more fuel to be contained within container 110 than in fuelcells having larger diaphragms. The border of the diaphragm need not bethe same as the valve plate 112, but should provide sufficientdeflection of the valve plate 112 for expected operating conditions ofthe power generator 100.

The fuel 130 may be formed in a pellet with multiple levelscorresponding to the area of the container without the recess, and thearea with the recess. In one embodiment, the fuel 130 is a pressedpellet utilizing LiAlH4 as the fuel. In further embodiments, one or morepellets may be used having a metal hydride, or combination of areas ofmetal hydride and chemical hydride to supply higher rates of hydrogenduring pulse power demand. Many different types of metal and chemicalhydrides to provide hydrogen in response to water vapor may be used infurther embodiments. One or more diffusion channels 131 may be providedin the fuel pellet in ensure penetration of water vapor and utilizationof a higher percentage of the fuel over the life of the power generator.The channels also allow the fuel pellet to expand without adverselydeforming container 110, and may be selected to be just wide enough forsuch expansion to optimize the volume of fuel that may be providedwithin a desired form factor. In one embodiment, channel 131 is anannular channel. Further channels or holes may be provided in variouspatterns through one or more fuel pellets to optimize water vaporpenetration.

In one embodiment, fuel cap 124 contains openings allowing water vaporand hydrogen to pass through. The openings are located within a radiusof the valve seat 128. A membrane 143, such as a Gore-Tex® membrane maybe disposed over the openings to serve as a particulate filter and ahydrogen and water vapor permeable, liquid water impermeable barrier toprevent water in liquid form from reaching the fuel. The fuel cap 124has an opening for the valve stem assembly 132.

In one embodiment, the valve stem assembly 134 includes an annulus 146disposed between the valve plate 112 and the diaphragm 136. The annulus146 may be cylindrical with internal threads on each end to mate withfasteners, such as screws 148, 150 for coupling the valve plate 112 anddiaphragm 136 respectively to the annulus 146. In one embodiment, thehead of the screw 150 may be reduced in height such that it isapproximately 1/16^(th) of an inch to provide more clearance formovement of the diaphragm without the screw 150 head moving outside thebottom of diaphragm support 138. In one embodiment, the screws haveapproximately 160 threads per inch. The screw 150 creates a gas sealabout the diaphragm 136 and annulus 146 in one embodiment.

The use of the annulus 146 and fasteners 148, 150 provides flexibilityin manufacturing, as either end may be assembled first. Opening 142 alsoprovides access to fastener 150, allowing the flexibility of fasteningthe diaphragm 136 to the valve stem assembly 132 when desired. Othertypes of fasteners, such as snap fit fasteners may also be used withsuitable modifications to the annulus 146 to mate with such snap fitfasteners 148, 150.

In one embodiment, fuel cell 114 is formed as a fuel cell stack havingmultiple layers, including a cathode electrode layer that is disposedproximate, yet insulated from the anode cap 118. Anode cap 118 hasopenings therein to allow oxygen to contact the cathode electrode layer,which as illustrated at 122, has an electrically conducting tabextending down to contact the fuel cap 124.

In one embodiment, the fuel cell 114 contains the following layersextending downward toward the fuel container in this embodiment. A 1 milEPTFE (expanded polytetrafluoroethylene) membrane, a 1 mil adhesive, 4mil adhesive and gas diffusion layer, Gore MEA (membrane electrodeassembly), 4 mil adhesive and gas diffusion layer and 2 mil Kapton®layer. This is followed by an optional porous compliant materialindicated at 152 to help keep the fuel cell in place. An open gap 153may be filled with epoxy or other material if desired.

In one embodiment, the EPTFE membrane may be used to prevent shortingproblems between the gas diffusion layer and anode cap 118. The membranemay be a dielectric gas permeable membrane that prevents shorts betweenanode cap 118 and the fuel cell stack. The next adhesive layer is adouble sided adhesive, such as a Kapton® membrane with adhesive on bothsides to hold adjacent layers of the fuel cell stack together andprovide a gas seal. The next Kapton layer serves as the cathodeelectrode. The layer has a gold surface with laser cut through holespatterned on it. Further detail is provided in the following figures.The adhesive and gas diffusion layer is like a frame of adhesive withinside regions cut out to expose the fuel cell membrane to gas. The fuelcell membrane may be a Gore MEA (membrane electrode assembly) thatserves as the active fuel cell membrane for the power generator 100. Thefollowing adhesive and gas diffusion layer and 2 mil Kapton® layer arealso patterned with gold, forming the anode electrode.

As shown in FIGS. 1 and 2, the anode electrode cap 118 contains twoannular ring posts 154, 156 defining an annular opening for the fuelcell 114. An outside annular post 158 forms an opening for mating withthe insulative insert 126, and also defines the outer diameter of theanode. The fuel cap 124 contains an annular portion 160 that mates witha top outside portion of the fuel container 110 which may contain achamfered edge 161 to provide for self alignment. The mating provides agas seal by use of epoxy, laser weld or other connection method.Similarly, sidewall 134 of container 110 may also have a chamfer to matein a self aligning manner with an internal annular edge 161 of the fuelcap 124.

FIGS. 3A, 3B, 3C, 3D, 3E and 3F are top views of various components thatmay be assembled to form the fuel cell 114 stack. FIG. 3A illustrates amembrane pattern 310 that may be duplicated such that five of them inone embodiment are disposed in a ring pattern in the stack. A ringshaped adhesive pattern is shown at 315 in FIG. 3B. Adhesive free areas317 are shown and are generally of the same shape as membrane patters310. A conductive layer 318 is disposed between the adhesive free areas,and may be formed of a conductor, such as gold. Conductive layer 318allows sections of the fuel cell to be electrically serially connected.Adhesive 319 is disposed on both sides of the adhesive pattern in theremaining portions of pattern 315.

FIG. 3C illustrates a cathode metallization pattern 325. Segmented metalareas 327 corresponding to the membrane pattern 310 are formed, alongwith metal free areas 328. A tab 330, corresponding to tab 122 in FIGS.1 and 2, is also formed with metal coating to provide the cathode tabfor connection to an external cathode for the power generator 100. FIG.3D illustrates a finished cathode electrode that includes five sectionsfor contacting 5 fuel cell membranes. The sections have holes 335 cutthrough the segmented metal areas 327 to allow gas diffusion to and fromthe fuel cell membrane.

FIGS. 3E and 3F show an anode metallization pattern 340 used to formanode electrode 345 respectively. Metallized segments 342 are formedwith holes 346. Non metal areas 348 are also indicated. An anodeelectrode tab 350, corresponding to tab 120 in FIGS. 1 and 2, is alsoformed and used to provide a connection to an external anode for thepower generator 100.

FIG. 4 is a cross sectional block schematic diagram illustratingelectrical connections between segments of fuel cell stacks indicatedgenerally at 400. Five segments of fuel cell stacks are illustrated,each having a cathode electrode 410, first adhesive and gas diffusionlayer 415, membrane electrode assembly 420, second adhesive and gasdiffusion layer 425 and anode electrode 430. Conductive tabs 435, suchas gold tabs, are provided between the segments, and provide a serieselectrical connection between stacks, connecting an anode of one stackto a cathode of the next stack. An anode electrode output tab 440,corresponding to tab 120 in FIGS. 1 and 2, is coupled to the anodeelectrode 430 of one stack, and a cathode electrode output tab 445,corresponding to tab 122 in FIGS. 1 and 2, is coupled to the cathodeelectrode 410 of a stack at the other end of the series connected serialstring of stacks.

In one embodiment, a method of manufacturing power generator 100 may beperformed by separately building top (cover 115) and bottom (container110) halves and creating an electrical coupling between them utilizingthe anode and cathode tabs 120, 122. The fuel cell 114 may be assembledas part of the anode. Part of the valve assembly 132 is placed withinthe fuel cap 124 that has an integrated valve seat 128. The anode 118and fuel cap 124 are then assembled with the “U” shaped electricalinsulator 126 between them to electrically isolate anode and cathode.The fuel pellet 130 is then inserted into the cathode/fuel container110, and the diaphragm support 138 and diaphragm 136 are assembled intothe fuel container recess 140 to maintain the CR2032 battery form factoror other desired form factor. After the fuel container bottom half 110and top half 115 containing the fuel cell 114 and valve assembly 132 areassembled together, a final screw 150 or snap fit is used to secure thediaphragm 136 to the rest of the valve assembly 132 though the hole 142in the bottom of the anode. Some of the assembly steps described hereinmay be performed in a different order than that presented. For instance,the fuel pellet may be inserted in the container 110 well before, duringor after assembly of the top half of the fuel cell. In furtherembodiments, the anode 118 may be the last element coupled to the fuelcell, with screw 148 being attached just prior to coupling of the anode118.

CONCLUSION

A hydrogen fuel cell based power generator has a self regulating valveassembly in a low height profile. A valve plate has a smaller borderthan the border of the power generator, with a fuel cell laterallydisposed in a somewhat coplanar ring or other shape around the valveplate. A valve assembly diaphragm also has a smaller border, making roomfor a larger, multi-level shaped fuel pellets that partially surroundthe diaphragm. Both of these arrangements combine to provide sufficientvalve movement within the form factor height limits, and also allow morefuel to be on board for a power generator with high energy content.

An annulus (threaded cylinder) may be used to which the valve plate anddiaphragm are attached on opposite ends by fasteners, such as screws orsnap fit members to clamp them in place. The annulus/fasteners provide avalve pin or stem function. The structure allows for manufacturabilitygiven the small form factor.

A method of manufacturing may be performed by separately building topand bottom halves and creating an electrical coupling between them. Thefuel cell is assembled as part of the cathode, and part of the valve ispositioned proximate a fuel cap that has an integrated valve seat. Thecathode and fuel cap are then assembled with a “U” shaped electricalinsulator between them to electrically isolate anode and cathode. Thefuel pellet is then inserted into the anode/fuel container, and adiaphragm support and diaphragm are assembled into the fuel container tomaintain the CR2032 form factor. After the fuel container bottom halfand top half containing the fuel cell and valve parts are assembledtogether, a final fastener such as a screw or snap fit may be used tosecure the diaphragm to the rest of the valve assembly though a hole inthe bottom of the anode.

The Abstract is provided to comply with 37 C.F.R. §1.72(b) to allow thereader to quickly ascertain the nature and gist of the technicaldisclosure. The Abstract is submitted with the understanding that itwill not be used to interpret or limit the scope or meaning of theclaims.

1. A device comprising: an annulus having a first end and a second end;a container adapted to hold a hydrogen producing fuel and having acover; a valve plate located above a portion of the container that holdsthe hydrogen producing fuel coupled to the first end of the annulus by afastener, wherein the valve plate is adapted to contact a valve seatunder the cover of the hydrogen producing fuel container; and adiaphragm located adjacent to the bottom of the portion of the containerthat holds the hydrogen producing fuel coupled to the second end of theannulus by another fastener, wherein the annulus extends through theportion of the container that holds the hydrogen producing fuel locatedabove an opening formed by a diaphragm support and wherein the diaphragmmoves the valve plate relative to the valve seat responsive to adifference in pressure across the diaphragm.
 2. The device of claim 1wherein the diaphragm support couples the diaphragm to a recess in thecontainer to provide a gas seal.
 3. The device of claim 2 wherein thediaphragm support forms the opening providing access to the fastenercoupling the diaphragm to the second end of the annulus.
 4. The deviceof claim 3 wherein the fasteners are screws and the first and secondends of the annulus have internal threads suitable for coupling with thescrews.
 5. The device of claim 4 wherein the screw coupling thediaphragm to the second end of the annulus has a height reduced suchthat it does not extend outside of the recess in the container as thediaphragm moves.
 6. The device of claim 5 wherein the screws compriseheads shaved to minimize height.
 7. The device of claim 2 wherein thediaphragm support and container are electrically coupled.
 8. The deviceof claim 7 and further comprising an electrically conductive adhesivedisposed between the diaphragm support and the container.
 9. The deviceof claim 2 wherein the fastener coupling the diaphragm to the second endof the annulus has a height reduced such that it does not extend outsideof the recess in the container as the diaphragm moves.
 10. The device ofclaim 1 wherein the annulus is formed of stainless steel
 316. 11. Thedevice of claim 1 wherein the valve plate further comprises a layer ofmaterial disposed on a surface of the valve plate that contacts thevalve seat to prevent stiction and provide a seal.
 12. A valve assemblyfor a proton exchange membrane fuel cell based power generator, thevalve assembly comprising: an annulus having a first end and a secondend; a container adapted to hold a hydrogen producing fuel and having acover; a valve plate located above a portion of the container that holdsthe hydrogen producing fuel coupled to the first end of the annulus by afastener, wherein the valve plate is adapted to contact a valve seatunder the container cover, and wherein the valve plate has a bordersmaller than a border of the container cover to provide coplanar spacefor a fuel cell within the container cover; a diaphragm located adjacentto the bottom of the portion of the container that holds the hydrogenproducing fuel coupled to the second end of the annulus by anotherfastener, wherein the annulus extends through the portion of thecontainer that holds the hydrogen producing fuel located above anopening formed by a diaphragm support and wherein the diaphragm movesthe valve plate relative to the valve seat responsive to a difference inpressure across the diaphragm; and the diaphragm support couples thediaphragm to a recess in the container to provide a gas seal, whereinthe recess has a border that fits within a border of the container toenable extra fuel to be contained by the container.
 13. The device ofclaim 12 wherein the diaphragm support forms the opening providingaccess to the fastener coupling the diaphragm to the second end of theannulus.
 14. The device of claim 13 wherein the fasteners are screws andthe first and second ends of the annulus have internal threads suitablefor coupling with the screws and wherein the screw coupling thediaphragm to the second end of the annulus has a height reduced suchthat it does not extend outside of the recess in the container as thediaphragm moves.
 15. The device of claim 12 wherein the fastenercoupling the diaphragm to the second end of the annulus has a heightreduced such that it does not extend outside of the recess in thecontainer as the diaphragm moves.
 16. The device of claim 12 wherein thevalve plate further comprises a layer of material disposed on a surfaceof the valve plate that contacts the valve seat to prevent stiction andprovide a seal.
 17. A method comprising: coupling a valve plate locatedabove a portion of a container adapted to hold a hydrogen producing fuelto a first end of an annulus by a fastener, wherein the valve plate isadapted to contact a valve seat under a container cover; coupling adiaphragm located adjacent to the bottom of the portion of the containerthat holds the hydrogen producing fuel to a second end of the annulus byanother fastener, wherein the annulus extends through the portion of thecontainer that holds the hydrogen producing fuel located above anopening formed by a diaphragm support and wherein the diaphragm movesthe valve plate relative to the valve seat responsive to a difference inpressure across the diaphragm; and clamping the diaphragm to a recess inthe container to provide a gas seal.
 18. The method of claim 17 whereinthe diaphragm is clamped using a diaphragm support having the openingproviding access to the fastener coupling the diaphragm to the secondend of the annulus.
 19. The method of claim 18 wherein the fasteners arescrews and the first and second ends of the annulus have internalthreads suitable for coupling with the screws, and wherein the screwcoupling the diaphragm to the second end of the annulus has a heightreduced such that it does not extend outside of the recess in thecontainer as the diaphragm moves.
 20. The method of claim 18 wherein thediaphragm support and container are electrically coupled.